Most textiles are colored with dyes which fix chemically to the textile fabrics. Coloring of the fabric is achieved without a noticeable change in the feel of the fabric itself. The chemical composition of the dye varies according to the fabric used i.e., different dyes are required for different fabrics. Some fabrics contain a proportion of dye which is not sufficiently fixed to the fibres; this happens more frequently for blended fabrics. This residual dye is usually removed during the process of manufacturing the fabric; but if the residual dye is not removed completely, the action of water will wash out the unfixed dyes during washing. This can cause discoloration of the whole fabric. This phenomenon is called “Dye Bleeding”. Dye bleeding is normally seen with disperse dyes when used for dyeing polyester fabrics, although it may also be seen with fabric blends, such as polyester-cotton blends.
In case of polyester fabric printed with ink of plastisol type, the unfixed disperse dyes in the fabric has a tendency to dissolve in the plasticizer of the plastisol inks with or without the need of external heat that is normally used to cure the printed area. This is called leaching of the dyes into the plasticizer or plastisol ink. This phenomenon of leaching is known as “Dye Migration” and can cause discoloration of the fabric as well as the printed image. The printed image will change from its original color, which is undesirable. The potential for dye migration is often not evident following printing and curing, and can occur subsequently anytime, within a few hours to a number of weeks.
The plastisol inks are normally heated (cured) at temperatures above 140° C. The dye leaching effect may be more severe resulting in fast discoloration of the printed image, when the plastisol printed fabrics are heated to this high temperature.
The disperse dyes also have a tendency to sublimate when heated, turning from a solid dye particle directly to a gas. This process can be accelerated by solvation due to the plasticizer.
Hybrids of plastisol inks and water-based discharge inks were used to stop dye bleeding. These inks contained a blend of polyvinyl chloride (PVC), phthalate-containing plastisol and an activated water-based discharge ink. This type of ink is unstable and contains PVC and phthalates. Further, the activator for the discharge ink is based on Zinc Formaldehyde Sulphoxylate (ZFS). Even though the discharge agent is very efficient, the composition contains formaldehyde which is detrimental to human health and the environment.
Therefore, there is a need for an effective plastisol based composition, which will completely stop the dye migration from a dyed polyester blended cotton fabric or a 100% polyester fabric to the print.